A sheet processing system may be provided with a post-processing apparatus which carries out a post processing on a sheet on which an image is formed. The post-processing apparatus carries out, for example, a processing for punching a hole on a sheet, or a processing for binding sheets with a stapler. In the post processing apparatus, there is a device, like the stapler, which carries out a processing on a plurality of sheets. In order to carry out such a post processing on the plurality of sheets, a standby tray temporarily keeps the plurality of the sheets at a standby position.
A size (for example, A size, B size and the like) of the waiting sheet is provided to the standby tray. The standby tray adjusts positions of supports for supporting the sheet from sides based on the size provided.
In this manner, the standby tray adjusts the positions of the supports according to the size. However, when the sheet is conveyed the standby tray, a skew may be generated. Further, there are times when an incorrect size is detected, and the incorrect size is provided to the standby tray.
In a case in which the skew is generated or the size is incorrectly detected, a paper jam may occur.